The invention is in the field of optical scanning instruments employed for assessing the uniformity of perforated sheets, sheets of paper, plastics, glass and the like.
The measurements of the degree of light transmission through sheets of material, such as, perforated sheets where the light restriction characteristics are a function of the number and size of the perforations or the degree of transparency of paper, plastic, glass and the like, and particularly the measurement of localized variability in light transmission as an assessment of uniformity, has frequently been proposed in the past.
A number of instruments are available for the purpose and methods and are well developed for interpreting parameters of variations in terms of light level and the fluctuating component. It is usual practice to connect the light signal to an electrical output signal and to measure amplitude of the output signal.
The instruments generally comprise a system of illuminating the test sheet by a small light spot produced by an appropriate combination of lenses, a light-gathering system of lenses to focus the transmitted light on a photomultiplier as a light sensing element, a regulated D.C. power supply for the photomultiplier and illuminating source and electronic amplification and monitoring equipment. In general, the equipment is complex, expensive and can test only a small surface area with each test, three disadvantages which have limited their application to laboratory use.